docs(readme): add install and usage instructions

README.md

@@ -1,6 +1,57 @@
 # @joinnus-team/eslint-config
 
-Shared ESlint configurations for Joinnus organization.
+[![semantic-release](https://img.shields.io/badge/%20%20%F0%9F%93%A6%F0%9F%9A%80-semantic--release-e10079.svg)](https://github.com/joinnusteam/JARCH-eslint-config)
+![npm (scoped with tag)](https://img.shields.io/npm/v/%40joinnus-team/eslint-config/latest)
+
+Set of shared ESLint-opinionated configurations for the Joinnus organization.
+
+## Installing
+
+```sh
+yarn add -D @joinnus-team/eslint-config
+```
+
+Or:
+
+```sh
+npm add -D @joinnus-team/eslint-config
+```
+
+> Make sure `peerDependencies` are installed (npm >= 7 do this automatically).
+
+## Usage
+
+### ESLint config
+
+In your `.eslintrc.json`:
+
+```json
+{
+  "extends": "@joinnus-team/eslint-config/{preset}"
+}
+```
+
+Where `{preset}` is one of the [available presets](#available-presets-for-eslint).
+
+> Check out the [ESLint documentation](https://eslint.org/docs/latest/extend/shareable-configs#using-a-shareable-config) other formats to use shared configurations and override some configs.
+
+### Prettier config
+
+You also need to use the related prettier configuration.
+
+In your `.prettierrc.json`:
+
+```json
+"@joinnus-team/eslint-config/default-prettier-config"
+```
+
+## Available presets for ESLint
+
+The default export from this package offers rules for Node.js 16 and up. Other available presets are:
+
+- `node-erbium`: For Node.js 12 applications.
+- `node-fermium` For Node.js 14 applications.
+- `node-gallium` For Node.js 16 applications.
 
 ## Contributing guidelines